Bipolar plate comprising metal wire

ABSTRACT

A bipolar plate as subject of the invention comprises a polymer wall ( 420 ) and a first ( 430 ) and a second ( 440 ) electrode. The first electrode is positioned at a first side of the polymer wall and the second electrode is positioned at the second side of the polymer wall. The first and the second electrode are partially embedded in the polymer wall where they make electrical contact with each other in the polymer wall. At least one of the electrodes comprises a metal wire knitted fabric, which is partially embedded in the polymer wall.

FIELD OF THE INVENTION

The present invention relates to bipolar plates, especially for use inelectrochemical processes. The present invention also relates to methodsfor providing such bipolar plates

BACKGROUND OF THE INVENTION

Bipolar plates are well known for use in electrochemical processes, e.g.full cells. Reactors of electrochemical processes may comprise an anodeand a cathode chamber being separated from each other by means of aliquid and gas tight barrier. Meanwhile, an electrically conductiveelectrode is provided in this anode and cathode chamber.

The bipolar plate may act as a liquid and gas barrier between anode andcathode chamber.

In some cases, the electrodes from the anode side and the cathode sideare to be in electrical contact with each other. EP229473B1 describessuch a bipolar plate comprising a polymer wall and a first and a secondelectrode, each at one side of the polymer wall. The electrodes areprovided using an undulated, possibly perforated metal sheet or anundulated wire mesh, in the form of a woven structure. The electrodesare partially embedded in the polymer wall, and make electrical contactwith each other in the polymer wall.

The stiffness of the perforated metal plate, and the relative largeamount of metal to be anchored in the polymer wall, renders theembedding of the electrodes in the polymer wall relatively difficult,causing uncertainty with regard to the necessary contact of bothelectrodes in the polymer wall. The presence of such amount of metalsheet causes significant pressure drops necessary for evacuation ofdistribution of reactant gasses in the electrodes. It also causes thebipolar plate to have a relatively large weight.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a bipolar plate,which is an alternative for the bipolar plates presently known in theart. It is also an object of the present invention to facilitate theembedding of the electrodes in the polymer wall. It is also an object ofthe present invention to provide a bipolar plate having an improvedanchoring of the electrode to the polymer wall. It is also an object ofthe present invention to provide a bipolar plate having a more certaincontact of both electrodes in the polymer wall. It is further an objectof the present invention to provide a bipolar plate improving theevacuation of gasses obtained as a result of the electrochemicalreactions. It is also an object of the present invention to facilitatethe distribution of gasses being reactants for the electrochemicalreactions over the whole surface of the electrodes. It is an otherobject of the present invention to obtain a bipolar plate with improveddistribution of liquids used for the electrochemical reaction. It isstill an other object of the present invention to provide a bipolarplate with reduced weight. It is further an object of the presentinvention to provide a bipolar plate, which is less expensive toproduce.

A bipolar plate as subject of the invention comprises a polymer wall anda first and a second electrode. The first electrode is positioned at afirst side of the polymer wall, whereas the second electrode ispositioned at the second side of the polymer wall. Both electrodes arepartially embedded in the polymer wall, making electrical contact witheach other in this polymer wall. The bipolar plate as subject of theinvention is characterized in that at least one of the first or secondelectrodes comprises a metal wire knitted fabric, which is partiallyembedded in the polymer wall. Possibly both electrodes comprise metalwire knitted fabrics, which are partially embedded in the polymer wall.The electrodes may even consist of metal wire knitted fabric. Possiblyeach electrode comprises more than one layer of metal wire knittedfabric, all layers added one on top of the other. The layer closest tothe polymer wall is partially embedded in the polymer wall.

It was also found that the use of metal wire knitted fabrics, theembedding of the fabrics is facilitated and can be done in a moreaccurate way. It was also found that the use of a metal wire knittedfabric, who is partially embedded in the polymer wall, provides animproved anchoring of the electrode in the polymer wall. As bothelectrodes are partially embedded in the polymer wall and makeelectrical contact in the polymer wall, the improved anchoring resultsin a more certain electrical contact between the electrodes over time.

It was found that when bipolar plates as subject of the invention,comprising electrodes consisting of possibly more than one layer ofmetal wire knitted fabric for each electrode, are used inelectrochemical processes, the gasses obtained by the chemical reactionsmay more easily and with less pressure drop be evacuated from theelectrodes.

Also, it was found that in case gasses are used as reactants, suchgasses are distributed more easily and equally over the whole electrodevolume, requiring less pressure to be distributed. It was further foundthat liquids used during electrochemical reaction are distributed moreeasily and equally over the whole electrode volume. As less metal volumeis necessary to provide the electrodes as compared with undulated sheetsor alike, the bipolar plate is less heavy. The fact of comprising lessmetal volume may also decrease the production price of bipolar plates.

The metal wire knitted product, used to provide a bipolar plate assubject of the invention, is not necessarily to be undulated as for thebipolar plates of the prior art. Therefor one step in production ofbipolar plates may be avoided, further reducing production costs.

Metal wire having a diameter in the range of 0.05 mm to 0.5 mm may beused to provide the metal wire knitted fabrics. More preferred, metalwires with a diameter in the range of 0.05 mm to 0.3 mm, such as in therange of 0.05 mm to 0.25 mm or in the range of 0.05 mm to 0.1 mm may beused. As metal wire, metal wires out of Ni or Ni-alloy may be used.Alternatively titanium, titanium alloys, or stainless steel alloys, suchas alloys of the AISI 300-series or AISI 400-series may be used, e.g.AISI 302, AISI 304, AISI 310, AISI 316, AISI 316L, AISI 347, AISI 430,AISI 434 or AISI 444.

The polymer wall preferably is a polymer sheet. The thickness of thepolymer wall is preferably more than 0.5 mm but less than 5 mm. Theselection of the thickness may influence the gas and liquidimpermeability of the polymer wall, and may influence the diffusioncoefficient of gas molecules through the polymer wall.

As polymer wall, the polymer material used to provide the polymer wallis preferably selected from the group consisting of fluoro-polymers suchas polytetrafluorethylene, or polyolefines, such as e.g. polypropylene,polyethylene or high-density polyethylene, polyacetal or polysulfon.Most preferred, the polymer wall is a polymer sheet, being obtained byextrusion processes. Extruded polymer sheets guarantee to a largerextent the gas- and liquid-tightness.

The two electrodes, of which at least one comprises a metal wire knittedfabric, are embedded partially in the polymer wall. Most preferred, themetal wire knitted fabrics are laminated together with the polymer wall,which is preferably a polymer sheet. The depth of the embedding of oneof the metal wire knitted fabrics of the electrodes is chosen in such away that both electrodes contact each other in the polymer wall, soproviding electrical contact between the two electrodes.

In order to have still a part of the metal wire knitted fabric notembedded at both sides of the polymer wall, the thickness of the metalwire knitted fabric being more than half of the thickness of the polymerwall. Preferably, the metal wire knitted fabric has a thickness lessthan 5 mm.

The density of the metal wire knitted fabric is preferably less than10%.

The electrode may comprise additional elements next to the partiallyembedded metal wire knitted fabric, e.g. spacing elements or catalystcarrying elements. Possibly more than one layer of metal wire knittedfabric may be used for each electrode, one layer being on top of theother, as an example to provide sufficient volume to the electrode or toprovide the other elements of the electrode.

On one or both electrodes, a catalyst for use in the electrochemicalreaction may be present. E.g. a catalyst selected from the groupconsisting of Rh, Ru, Pt, Pd, Ir, Ag, Ni, Cu, WC or AU or combinationsthereof may be used. The catalyst on the first electrode may beidentical or different as the catalyst on the second electrode.

Possibly, the catalysts are only present at a certain zone of theelectrode. As an example, the catalyst may only be present at the sideof the electrode removed from the polymer wall.

As an example, an electrode may comprise a first metal wire knittedfabric, partially embedded in the polymer wall as subject of theinvention. A second metal wire knitted fabric functioning as spacinglayer between the first metal wire knitted fabric and the catalystcarrier is present on top of the first metal wire knitted fabric. On topof the second metal wire knitted fabric, a third metal fiber knittedfabric being coated with a catalyst, is provided functioning as catalystcarrier.

The bipolar plates as subject of the invention may be used in all kindsof electrochemical reactors, such as e.g. fuel cells, electrolysers orH₂-production units.

In case the electrode comprises more than one layer of metal wireknitted fabric, only some layers may be coated with a catalyst. Mostpreferred, the metal wire knitted fabric who is partially embedded inthe polymer wall is not coated with a catalyst.

It is further an object to provide a method of providing a bipolarplate, comprising the steps of

-   -   Providing a polymer wall;    -   Providing a first electrode comprising a metal wire knitted        fabric;    -   Providing a second electrode comprising a metal wire knitted        fabric;    -   Providing the first electrode at a first side of the polymer        wall;    -   Providing the second electrode at a second the of said polymer        wall;    -   Laminating the first and said second electrode and the polymer        wall.

The method provided bipolar plates in a more economic way, and in themean time it is easy to control, as some process parameters, e.g.pressure during lamination is less critical. The latter is due to theelasticity the metal wire knitted fabrics possess in a directionperpendicular to its surface.

Possibly the method of production of a bipolar plate as subject of theinvention further comprises the step of coating one or both of the metalwire knitted fabrics with a catalyst.

Possibly the method of production of a bipolar plate further comprisesthe step of adding different layers of metal wire knitted fabric one ontop of the other before or after laminating, in order to obtainelectrodes comprising more than one layer of metal wire knitted fabric.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described into more detail with reference tothe accompanying drawings wherein

FIG. 1 shows schematically a side view of a bipolar plate as subject ofthe invention;

FIG. 2 shows schematically a cross section according to plane AA′ of abipolar plate as subject of the invention of FIG. 1.

FIG. 3 and FIG. 4 show schematically a cross section of alternativebipolar plates as subject of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

A side view of a bipolar plate 110 as subject of the invention is shownin FIG. 1. A polymer wall 120 has two outer surfaces, and at least inone surface 121, a metal wire knitted fabric 130 being part of anelectrode is partially embedded in the polymer wall 120. At the otherside 122 of the polymer wall 120, possibly another metal wire knittedfabric 140 (not shown for reason of clarity in FIG. 1) being part of theelectrode at the other side 122 is partially embedded in the polymerwall 120.

FIG. 2 shows a cross section of the bipolar plate 110, having twoelectrodes comprising metal wire knitted fabric (130 and 140), one ateach side of the polymer wall 120.

A bipolar plate 110 comprises a polymer wall 120 with a thickness 221,e.g. 2 mm. At both sides 121 and 122 of the polymer wall 120, preferablyan extruded HDPP, HDPE, polysulfon or polyacetal sheet, a metal wireknitted fabric 130 and 140 is partially embedded over a depth ofslightly more than half of the thickness 221 of the polymer wall 120. Itis understood that the thickness 233 and 243 of the metal wire knittedfabrics is to be substantially more than this half of the thickness 221of the polymer wall 120, in order to provide a significant volume to theelectrode which is not embedded in the polymer wall, providing voidvolume to the electrodes for gas evacuation of supply of reactant gas orreactant liquid.

Possibly, the metal wire knitted fabric 130 may be coated with acatalyst based on Pt and Ru. The metal wire knitted fabric 140 may becoated with a catalyst based on Pt and Ir.

The metal wire knitted fabrics 130 and 140 may be a double bed knittedstructure (either warp of weft knitted) using a machine gauge of 5 (5needles per inch of needle bed). A nickel wire of diameter 250 μm may beused.

The metal wire knitted fabric is preferably embedded in the polymerwall, being preferably a polymer sheet, by laminating the knitted fabricin the sheet.

A cross section of an alternative bipolar plate as subject of theinvention is shown in FIG. 3.

The bipolar plate 310 comprises a polymer wall 320, being an extrudedpolymer sheet of high-density polypropylene (HDPP), polysulfon,polyacetal or high-density polyethylene (HDPE). The thickness 321 of thepolymer sheet is approximately 1 mm. At one side of the polymer wall311, a first electrode 330 is located, comprising two layers of metalwire knitted fabric (indicated 331 and 332), the layer of metal wireknitted fabric 331, closest to the polymer wall 320 is partiallyembedded in the polymer wall 320. The thickness of the electrode(indicated 333), being the sum of thickness of layer 331 and layer 332,is approximately 7 mm, wherein each layer 331 and 332 has a thickness ofapproximately 3.5 mm.

Layer 331 is embedded in polymer wall over a depth of slightly more than0.5 mm.

At the other side 312 of the polymer wall, a second electrode 340 islocated, comprising two layers of metal wire knitted fabric (indicated341 and 342), the layer of metal wire knitted fabric 341, closest to thepolymer wall 320 is partially embedded in the polymer wall 320. Thethickness of the electrode (indicated 343), being the sum of thicknessof layer 341 and layer 342, is approximately 7 mm, wherein each layer341 and 342 has a thickness of approximately 3.5 mm.

Layer 341 is embedded in polymer wall over a depth of slightly more than0.5 mm.

As both metal wire knitted products 331 and 341 are embedded using adepth of slightly more than half of the thickness 321 of the polymerwall, an electrical contact between both metal wire knitted fabrics 331and 341, and thus between both electrodes 330 and 340 is ensured.

As an example, the metal wire knitted fabrics 331, 332, 341, and 341 maybe a single jersey knitted structure using a machine gauge of 5 (5needles per inch of needle bed). A nickel wire of diameter 250 μm may beused, providing a metal wire knitted fabric having a thickness ofapproximately 3.5 mm, having a weight of 47.5 g/m² and density of 1.7%

Possibly, the layer 332 may be coated with a catalyst based on Pt andIn. The layer 342 may be coated with a catalyst based on Pt and Ir.

A cross section of an alternative bipolar plate as subject of theinvention is shown in FIG. 4.

The bipolar plate 410 comprises a polymer wall 420, being an extrudedpolymer sheet of high-density polypropylene (HDPP), polysulfon,polyacetal or high-density polyethylene (HDPE). The thickness 421 of thepolymer sheet is approximately 1 mm. At one side of the polymer wall411, a first electrode 430 is located, comprising three layers of metalwire knitted fabric (indicated 431, 432 and 433), the layer of metalwire knitted fabric 431, closest to the polymer wall 420 is partiallyembedded in the polymer wall 420. The thickness of the electrode(indicated 434), being the sum of thickness of layer 431, layer 432 andlayer 433, is approximately 10.5 mm, wherein each layer 431, 432 and 433has a thickness of approximately 3.5 mm.

Layer 431 is embedded in polymer wall over a depth of slightly more than0.5 mm.

At the other side 412 of the polymer wall, a second electrode 440 islocated, comprising three layers of metal wire knitted fabric (indicated441, 442 and 443), the layer of metal wire knitted fabric 441, closestto the polymer wall 420 is partially embedded in the polymer wall 420.The thickness of the electrode (indicated 444), being the sum ofthickness of layers 441, 442 and 443, is approximately 10.5 mm, whereineach layer 341 and 342 has a thickness of approximately 3.5 mm.

Layer 441 is embedded in polymer wall over a depth of slightly more than0.5 mm.

As both metal wire knitted products 431 and 441 are embedded using adepth of slightly more than half of the thickness 421 of the polymerwall, an electrical contact between both metal wire knitted fabrics 431and 441, and thus between both electrodes 430 and 440 is ensured.

The metal wire knitted fabrics 441, 442, 443, 431, 432 and 433, may beidentical as the metal wire knitted fabric used for the embodiment asshown in FIG. 3.

The metal wire knitted fabrics 432 and 442 function as spacing layersbetween the first metal wire knitted fabrics 431 and 441, and the thirdmetal wire knitted fabrics 433 and 443, which are coated with a catalystbased on Pt and In for metal wire knitted fabric 433 and a catalystbased on Pt and Ir for metal wire knitted fabric 443.

1. A bipolar plate comprising a polymer wall which comprises a firstside and a second side, said plate further comprising a first and asecond electrode, said first electrode positioned at said first side ofsaid polymer wall, said second electrode positioned at said second sideof said polymer wall, said first and said second electrode beingpartially embedded in said polymer wall, said first and said secondelectrode making electrical contact with each other in said polymerwall, characterized in that at least one of said first or secondelectrode comprises a metal wire knitted fabric, being partiallyembedded in said polymer wall.
 2. A bipolar plate as in claim 1, whereinsaid first and said second electrode comprise a metal wire knittedfabric being partially embedded in said polymer wall.
 3. A bipolar plateas in claim 1, wherein said electrodes consist of metal wire knittedfabrics.
 4. A bipolar plate as in claim 1, wherein said first and saidsecond electrode comprise more than one layer of wire knitted fabric,only one of said layers of metal wire knitted fabric of each of saidelectrodes being partially embedded in said polymer wall.
 5. A bipolarplate as in claim 1, wherein said metal wire knitted fabric has adensity of less than 10%.
 6. A bipolar plate as in claim 1, wherein saidpolymer wall is a polymer sheet.
 7. A bipolar plate as in claim 6,wherein said polymer sheet is an extruded polymer sheet.
 8. A bipolarplate as in claim 1, wherein said metal wire knitted fabric is providedusing Ni or Ni-alloy metal wire.
 9. A bipolar plate as in claim 1,wherein said metal wire knitted fabric comprises metal wire having adiameter of less than 0.5 mm
 10. A bipolar plate as in claim 1, whereinsaid polymer wall is provided using a polymer material selected from thegroup consisting of fluoro-polymers, polyolefines, or polyacetal orpolysulfon.
 11. A bipolar plate as in claim 1, wherein said polymer wallhas a thickness of more than 0.5 mm, said polymer wall having athickness of less than 5 mm.
 12. A bipolar plate as in claim 1, whereinsaid first and said second electrode each has a thickness of more thanhalf of the thickness of said polymer wall.
 13. A bipolar plate as inclaim 1, wherein said first electrode and/or said second comprises acatalyst.
 14. A bipolar plate as in claim 1, wherein said first and/orsaid second electrode comprises a catalyst selected from the groupconsisting of Rh, Ru, Pt, Pd, Ir, Ag, Ni, Cu, WC or Au or combinationsthereof.
 15. A method to provide a bipolar plate, said method comprisingthe steps of Providing a polymer wall; Providing a first electrodecomprising a metal wire knitted fabric; Providing a second electrodecomprising a metal wire knitted fabric; Providing said first electrodeat a first side of said polymer wall; Providing said second electrode ata second side of said polymer wall; Laminating said first and saidsecond electrode and said polymer wall.
 16. The use of a bipolar plateas in claim 1 in electrochemical reactors.
 17. The use of a bipolarplate as in claim 1 for production of H₂.